The present invention relates generally to musical instruments and more particularly to a polyphonic periodic-signal synthesizer and to polyphonic electronic musical instruments comprising one or more such synthesizers.
There exist constantly increasing numbers of musical instruments in which electronic techniques are utilised to produce musical signals. The most traditional of these is the monophonic or polyphonic electronic organ, which utilises either analog techniques or digital techniques, or more often a mixture of both. Usually, in polyphonic instruments, a set of oscillators and dividers generate a large number of periodic signals having specific spectral characteristics. A set of keys, buttons and pedals actuated by the user of the instrument select one or more periodic signals and transmit them to filtering circuits intended to modify their spectral characteristics as a function of the positions of stop control members and sometimes as a function of time. The richness of the sounds produced depends upon the complexity of the circuits and the polyphonic character of the instrument involves a multiplication of the circuits, controls and wiring, and hence of the cost.
The use of digital techniques makes it possible to reduce the complexity of the wiring at the level of the keyboards and of the controls, for example by using a method of sequentially scanning the various keys, buttons, levers and pedals. However, there are always material and direct coupling means between these control means, the signal-generating circuits and the filtering circuits, so that the creation of a novel instrument, or the modification of the characteristics of an existing instrument, involve a substantially complete new study of the circuits and considerable work on the material plane.